Inhibition of myosin ATPase by metal fluoride complexes

Aluminum Fluorides as Noncovalent Lewis Acids in Proteins: The Case of Phosphoryl Transfer Enzymes

The Protein Data Bank (PDB) was scrutinized for the presence of noncovalent O ⋅ ⋅ ⋅ Al Triel Bonding (TrB) interactions, involving protein residues (e. g. GLU and GLN), adenosine/guanine diphosphate moieties (ADP and GDP), water molecules and two aluminum fluorides (AlF3 and AlF4 -). The results were statistically analyzed, revealing a vast number of O ⋅ ⋅ ⋅ Al contacts in the active sites of phosphoryl transfer enzymes, with a marked directionality towards the Al σ-/π-hole. The physical nature of the TrBs studied herein was analyzed using Molecular Electrostatic Potential (MEP) maps, the Quantum Theory of Atoms in Molecules (QTAIM), the Non Covalent Interaction plot (NCIplot) visual index and Natural Bonding Orbital (NBO) studies. As far as our knowledge extends, it is the first time that O ⋅ ⋅ ⋅ Al TrBs are analyzed within a biological context, participating in protein trapping mechanisms related to phosphoryl transfer enzymes. Moreover, since they are involved in the stabilization of aluminum fluorides inside the protein's active site, we believe the results reported herein will be valuable for those scientists working in supramolecular chemistry, catalysis and rational drug design.

Metal fluorides-multi-functional tools for the study of phosphoryl transfer enzymes, a practical guide

Enzymes facilitating the transfer of phosphate groups constitute the most extensive protein families across all kingdoms of life. They make up approximately 10% of the proteins found in the human genome. Understanding the mechanisms by which enzymes catalyze these reactions is essential in characterizing the processes they regulate. Metal fluorides can be used as multifunctional tools to study these enzymes. These ionic species bear the same charge as phosphate and the transferring phosphoryl group and, in addition, allow the enzyme to be trapped in catalytically important states with spectroscopically sensitive atoms interacting directly with active site residues. The ionic nature of these phosphate surrogates also allows their removal and replacement with other analogs. Here, we describe the best practices to obtain these complexes, their use in NMR, X-ray crystallography, cryo-EM, and SAXS and describe a new metal fluoride, scandium tetrafluoride, which has significant anomalous signal using soft X-rays.

Fluoride as a Potential Repressor of Glycogen Metabolism in Skeletal Muscle Cell Line CCL136

The exposure of humans to fluorine is connected with its presence in the air, food and water. It is well known that fluorides even at a low concentration but with long time exposure accumulate in the body and lead to numerous metabolic disorders. Fluoride is recognised as a factor modulating the energy metabolism of cells. This interaction is of particular importance in muscle cells, which are cells with high metabolic activity related to the metabolism of glucose and glycogen. In someone suffering from chronic fluoride poisoning, frequent symptoms are chronic fatigue not relieved by extra sleep or rest, muscular weakness, muscle spasms, involuntary twitching. The aim of this study was to examine the effect of fluorine at concentrations determined in blood of people environmentally exposed to fluorides on activity and expression of enzymes taking part in metabolism of muscle glycogen. CCL136 cells were cultured under standard conditions with the addition of NaF. The amount of ATP produced by the cells was determined using the HPLC method, the amount and expression of genes responsible for glycogen metabolism using WB and RT PCR methods and the amount of glycogen in cells using the fluorimetric and PAS methods. It has been shown that in CCL136 cells exposed to 1, 3 and 10 μM NaF there is a change in the energy state and expression pattern of enzymes involved in the synthesis and breakdown of glycogen. It was observed that NaF caused a decrease in ATP content in CCL136 cells. Fluoride exposure also increased glycogen deposition. These changes were accompanied by a decrease in gene expression and the level of enzymatic proteins related to glycogen metabolism: glycogen synthase, glycogen synthase kinase and glycogen phosphorylase. The results obtained shed new light on the molecular mechanisms by which fluoride acts as an environmental toxin.

A comprehensive review on endemic and experimental fluorosis in sheep: Its diverse effects and prevention

Fluoride is a natural element widely distributed in the environment and plays an important role in the growth of humans and animals. However, in many species, high concentrations of fluoride induce several problems, such as dental, skeletal, and non-skeletal fluorosis. Sheep living in endemic areas are sensitive to the chronic toxicity of fluoride, and they have been found to suffer not only from teeth and bone problems but also from other organs. Studies indicating the chronic harmful effects of fluoride on teeth, bones, blood biochemical parameters, kidney, liver, heart, reproductive system and growth in sheep have been clearly summarized in this review. Besides, this work also includes updated progress in terms of prevention or reduction of fluoride toxicity in this species.

Effects of Fluoride on Submandibular Glands of Mice: Changes in Oxidative Biochemistry, Proteomic Profile, and Genotoxicity

Although fluoride (F) is well-known to prevent dental caries, changes in cell processes in different tissues have been associated with its excessive exposure. Thus, this study aimed to evaluate the effects of F exposure on biochemical, proteomic, and genotoxic parameters of submandibular glands. Twenty one old rats (n = 30) were allocated into three groups: 60 days administration of drinking water containing 10 mgF/L, 50 mgF/L, or only deionized water (control). The submandibular glands were collected for oxidative biochemistry, protein expression profile, and genotoxic potential analyses. The results showed that both F concentrations increased the levels of thiobarbituric acid–reactive substances (TBARS) and reduced glutathione (GSH) and changed the proteomic profile, mainly regarding the cytoskeleton and cellular activity. Only the exposure to 50 mgF/L induced significant changes in DNA integrity. These findings reinforce the importance of continuous monitoring of F concentration in drinking water and the need for strategies to minimize F intake from other sources to obtain maximum preventive/therapeutic effects and avoid potential adverse effects.

Sodium fluoride induced skeletal muscle changes: Degradation of proteins and signaling mechanism

Fluoride is a well-known compound for its usefulness in healing dental caries. Similarly, fluoride is also known for its toxicity to various tissues in animals and humans. It causes skeletal fluorosis leading to osteoporosis of the bones. We hypothesized that when bones are affected by fluoride, the skeletal muscles are also likely to be affected by underlying molecular events involving myogenic differentiation. Murine myoblasts C2C12 were cultured in differentiation media with or without NaF (1 ppm-5 ppm) for four days. The effects of NaF on myoblasts and myotubes when exposed to low (1.5 ppm) and high concentration (5 ppm) were assessed based on the proliferation, alteration in gene expression, ROS production, and production of inflammatory cytokines. Changes based on morphology, multinucleated myotube formation, expression of MyHC1 and signaling pathways were also investigated. Concentrations of NaF tested had no effects on cell viability. NaF at low concentration (1.5 ppm) caused myoblast proliferation and when subjected to myogenic differentiation it induced hypertrophy of the myotubes by activating the IGF-1/AKT pathway. NaF at higher concentration (5 ppm), significantly inhibited myotube formation, increased skeletal muscle catabolism, generated reactive oxygen species (ROS) and inflammatory cytokines (TNF-α and IL-6) in C2C12 cells. NaF also enhanced the production of muscle atrophy-related genes, myostatin, and atrogin-1. The data suggest that NaF at low concentration can be used as muscle enhancing factor (hypertrophy), and at higher concentration, it accelerates skeletal muscle atrophy by activating the ubiquitin-proteosome pathway.

Amelioration of the Protein Expression of Cox2, NFB, and STAT-3 by Some Antioxidants in the Liver of Sodium Fluoride-Intoxicated Rats

The present study aimed to explore the efficiency of N-acetyl cysteine (NACC) or thymoquinone (TMQ) alone or in combination in the downregulation of inflammatory molecule expression and decreasing hepatic injury in response to sodium fluoride (SF). Sodium fluoride upregulated serum alanine and aspartate transferases activities, tumor necrosis factor α and hepatic malondialdehyde and nitric oxide levels, and the expression of cyclooxygenase 2, nuclear factor κB cell, and signal transducer and activator of transcription 3. In contrast, hepatic glutathione level, superoxide dismutase activity, and nuclear factor erythroid 2-related factor 2 expression were decreased. However, the concurrent treatment with antioxidants, alone or in combination, modulated the levels of these parameters. Histopathological examination revealed that SF treatment resulted in focal areas of massive hepatic degeneration and many degenerated hepatocytes, whereas the treatment with TMQ or NACC exhibited moderate improvement in cellular degeneration of the liver with many abnormal cells. Rats receiving a combination of TMQ and NACC showed marked improvement in cellular degeneration of liver with apparently normal hepatic architecture with very few degenerated hepatocytes. The results also revealed that the combination of TMQ and NACC is the most effective regimen in ameliorating SF toxicity, suggesting their efficacy against the toxicity of fluoride compounds. Their activities might be mediated via multiple molecular pathways.

Hydrolysis of diadenosine polyphosphates. Exploration of an additional role of Mycobacterium smegmatis MutT1

Diadenosine polyphosphates (Ap_nA, n=2-6), particularly Ap₄A, are involved in several important physiological processes. The substantial sequence identity of the Nudix hydrolase domain (domain 1) of Mycobacterium smegmatis MutT1 (MsMutT1) with a known Ap₄A hydrolase suggested that MsMutT1 could also hydrolyse diadenosine polyphosphates. Biochemical experiments yielded results in conformity with this suggestion, with Ap₄A as the best among the substrates. ATP is a product in all experiments; small amounts of ADP were also observed in the experiments involving Ap₄A and Ap₆A. Hydrolysis was inhibited by fluoride ions in all cases. The mechanism of action and its inhibition in relation to Ap_nA were explored through the X-ray analysis of the crystals of the MsMutT1 complexes with Ap₅A; Ap₅A and MnCl₂; Ap₄A; ATP; and ATP.NaF.MgCl₂. The aggregation pattern of molecules in the first four crystals is similar to that found in a majority of MsMutT1-NTP crystals. Substrate molecules occupy the primary binding site and ATP occupies a site at an intermolecular interface, in the first two. ATP occupies both the sites in the third and fourth crystal. The protein-ligand interactions observed in these crystal structures lead to an explanation of the molecular mechanism of hydrolysis of Ap_nA by MsMutT1. The fifth crystal exhibits a new packing arrangement. The structure of the complex provides an explanation for the fluoride inhibition of the activity of the enzyme. It would thus appear that MutT1 has a major role involving the hydrolysis of diadenosine polyphosphates, which could be elucidated at the molecular level.

Mg²⁺ coordinating dynamics in Mg:ATP fueled motor proteins

The coordination of Mg(2+) with the triphosphate group of adenosine triphosphate (ATP) in motor proteins is investigated using data mining and molecular dynamics. The possible coordination structures available from crystal data for actin, myosin, RNA polymerase, DNA polymerase, DNA helicase, and F1-ATPase are verified and investigated further by molecular dynamics. Coordination states are evaluated using structural analysis and quantified by radial distribution functions, coordination numbers, and pair interaction energy calculations. The results reveal a diverse range of both transitory and stable coordination arrangements between Mg(2+) and ATP. The two most stable coordinating states occur when Mg(2+) coordinates two or three oxygens from the triphosphate group of ATP. Evidence for five-site coordination is also reported involving water in addition to the triphosphate group. The stable states correspond to a pair interaction energy of either ∼-2750 kJ/mol or -3500 kJ/mol. The role of water molecules in the hydration shell surrounding Mg(2+) is also reported.

Activation of phospholipase A(2) by low levels of fluoride in THP1 macrophages via altered Ca(2+) and cAMP concentration

Phospholipases (PLA's) participate in the regulation of physiological and pathological processes in the cell, including the release of pro-inflammatory mediators and stimulation of inflammatory processes. It is also well known that fluoride can increase the inflammatory reactions. Therefore we decided to examine the effect of fluorides in concentrations determined in human serum on cPLA(2) and sPLA(2) activity. The incubation of macrophages in fluoride solutions significantly increased the amount of synthesized cellular cAMP, intracellular calcium and sPLA(2) activity in a dose-dependent pattern. The cPLA(2) activity, estimated by the amount of released arachidonic acid, increased significantly when 10 μM NaF was used. The results of our study suggest that fluoride may change the activity of phospholipases in macrophage cells. Probably, increased cAMP concentration activates protein kinase C (PKC) and thus stimulates PLA(2). cAMP also regulates the passage of Ca(2+) through ion channels, which additionally influence PLA(2) throughout Ca(2+)-calmodulin dependent protein kinase.

Modulation of lipid peroxidation and antioxidant defense systems in rat intestine by subchronic fluoride and ethanol administration

Excessive consumption of fluoride and ethanol has been identified as injurious to human health. Fluoride and ethanol co-exposures are commonly seen among the alcoholics residing in endemic fluoride areas worldwide. This study was undertaken to examine the modulation of lipid peroxidation and antioxidant defense systems in rat intestine by subchronic fluoride and ethanol administration. Female Sprague-Dawley rats were divided into four groups: group I (control), group II (fluoride was given orally at a dose of 25 mg/kg body weight), group III (30% ethanol was given orally at a dose of 1 mL/kg body weight), and group IV (a combination of fluoride and ethanol was administered orally at the dose described for groups II and III). Lipid peroxidation was elevated (P<.05) in intestine of rats by fluoride or ethanol treatments for 20 or 40 days. However, glutathione content was reduced by fluoride (32 and 44%) and ethanol (21 and 40%) treatments after 20 and 40 days, respectively. Fluoride-exposed animals showed reduction (P<.05) in the activities of superoxide dismutase (22 and 42%), catalase (30 and 37%), glutathione peroxidase (22 and 35%), glutathione reductase (32 and 34%), and glutathione-S-transferase (24 and 30%) after 20 and 40 days. A similar decrease (P<.05) in the activities of these enzymes was also noticed in animals exposed to ethanol for 20 or 40 days. The observed changes in lipid peroxidation, reduced glutathione levels, and enzyme systems were further augmented in intestine of rats exposed to fluoride and ethanol together. Intestinal histology showed large reactive lymphoid follicles along with mild excess of lymphocytes in lamina propria of villi, villous edema, focal ileitis, and necrosis of villi in animals exposed to fluoride and ethanol for 40 days. These findings suggest that fluoride and ethanol exposure induces considerable changes in lipid peroxidation, antioxidant defense, and morphology of rat intestine, which may affect its functions.

DNA-induced narrowing of the gyrase N-gate coordinates T-segment capture and strand passage

DNA gyrase introduces negative supercoils into DNA in an ATP-dependent reaction. DNA supercoiling is catalyzed by a strand-passage mechanism, in which a T-segment of DNA is passed through the gap in a transiently cleaved G-segment. Strand passage requires the coordinated closing and opening of three protein interfaces in gyrase, the N-gate, DNA-gate, and C-gate. We show here that DNA binding to the DNA-gate of gyrase and wrapping of DNA around the C-terminal domains of GyrA induces a narrowing of the N-gate. This half-closed state prepares capture of a T-segment in the upper cavity of gyrase. Subsequent N-gate closure upon binding of ATP then poises the reaction toward strand passage. The N-gate reopens after ATP hydrolysis, allowing for further catalytic cycles. DNA binding, cleavage, and wrapping and N-gate narrowing are intimately linked events that coordinate conformational changes at the DNA and the N-gate.

The sarcoplasmic Ca2+-ATPase: design of a perfect chemi-osmotic pump

The sarcoplasmic (SERCA 1a) Ca2+-ATPase is a membrane protein abundantly present in skeletal muscles where it functions as an indispensable component of the excitation-contraction coupling, being at the expense of ATP hydrolysis involved in Ca2+/H+ exchange with a high thermodynamic efficiency across the sarcoplasmic reticulum membrane. The transporter serves as a prototype of a whole family of cation transporters, the P-type ATPases, which in addition to Ca2+ transporting proteins count Na+, K+-ATPase and H+, K+-, proton- and heavy metal transporting ATPases as prominent members. The ability in recent years to produce and analyze at atomic (2·3-3 Å) resolution 3D-crystals of Ca2+-transport intermediates of SERCA 1a has meant a breakthrough in our understanding of the structural aspects of the transport mechanism. We describe here the detailed construction of the ATPase in terms of one membraneous and three cytosolic domains held together by a central core that mediates coupling between Ca2+-transport and ATP hydrolysis. During turnover, the pump is present in two different conformational states, E1 and E2, with a preference for the binding of Ca2+ and H+, respectively. We discuss how phosphorylated and non-phosphorylated forms of these conformational states with cytosolic, occluded or luminally exposed cation-binding sites are able to convert the chemical energy derived from ATP hydrolysis into an electrochemical gradient of Ca2+ across the sarcoplasmic reticulum membrane. In conjunction with these basic reactions which serve as a structural framework for the transport function of other P-type ATPases as well, we also review the role of the lipid phase and the regulatory and thermodynamic aspects of the transport mechanism.

What can be learned about the function of a single protein from its various X-ray structures: the example of the sarcoplasmic calcium pump

Improvements in the handling of membrane proteins for crystallization, combined with better synchrotron sources for X-ray diffraction analysis, are leading to clarification of the structural details of an ever increasing number of membrane transporters and receptors. Here we describe how this development has resulted in the elucidation at atomic resolution of a large number of structures of the sarcoplasmic Ca(2+)-ATPase (SERCA1a) present in skeletal muscle. The structures corresponding to the various intermediary states have been obtained after stabilization with structural analogues of ATP and of metal fluorides as mimicks of inorganic phosphate. From these results it is possible, in accordance with previous biochemical and molecular biology data, to give a detailed structural description of both ATP hydrolysis and Ca(2+) transport through the membrane, to serve as the starting point for a fuller understanding of the pump mechanism and, in future studies, on the regulatory role of this ubiquitous intracellular Ca(2+)-ATPase in cellular Ca(2+) metabolism in normal and pathological conditions.

The DEAD box helicase YxiN maintains a closed conformation during ATP hydrolysis

DEAD box helicases unwind RNA duplexes at the expense of ATP hydrolysis. Recently, unwinding has been demonstrated in the absence of ATP hydrolysis. Herein, we show that ADP.BeF(x) supports RNA unwinding by YxiN, a DEAD box helicase that specifically recognizes a hairpin in 23S rRNA. ADP.AlF(x) and ADP.MgF(x) do not promote RNA unwinding, but all ATP analogues induce a closed conformation of the helicase core as required for RNA unwinding. Our results show that the interdomain cleft in the helicase core closes upon ATP binding at the beginning of the cycle. Reopening occurs after ATP hydrolysis, most likely coupled to phosphate release.

Alterations in biochemical parameters during subacute toxicity of fluoride alone and in conjunction with aluminum sulfate in goats

Fluoride toxicity is a serious health problem in many parts of the globe. In present study, sodium fluoride at 20 mg/kg alone and in conjunction with aluminum sulfate at 150 mg/kg was administered orally daily for 30 days in healthy goats of group 1 and 2, respectively, to access the alterations in the various biochemical parameters during subacute toxicity of fluoride alone and in conjunction with aluminum sulfate. In Group 1, significant alterations in plasma glucose, blood urea nitrogen (BUN), creatinine, total protein, albumin, globulin, albumin/globulin ratio, magnesium, and sodium were observed on different days of exposure from their pre-exposure values. However, no significant changes were observed in plasma calcium, phosphorus, and potassium on different days of exposure of sodium fluoride. Similar type of biochemical alterations were noticed in the goats of Group 2 except BUN, total protein magnesium, and sodium. On the basis of results, it could be concluded that sodium fluoride alone and in conjunction with aluminum sulfate produced significant alterations in the various biochemical parameters of the body.

Interaction of asymmetric ABCC9-encoded nucleotide binding domains determines KATP channel SUR2A catalytic activity

Nucleotide binding domains (NBDs) secure ATP-binding cassette (ABC) transporter function. Distinct from traditional ABC transporters, ABCC9-encoded sulfonylurea receptors (SUR2A) form, with Kir6.2 potassium channels, ATP-sensitive K+ (K ATP) channel complexes. SUR2A contains ATPase activity harbored within NBD2 and, to a lesser degree, NBD1, with catalytically driven conformations exerting determinate linkage on the Kir6.2 channel pore. While homodomain interactions typify NBDs of conventional ABC transporters, heterodomain NBD interactions and their functional consequence have not been resolved for the atypical SUR2A protein. Here, nanoscale protein topography mapped assembly of monodisperse purified recombinant SUR2A NBD1/NBD2 domains, precharacterized by dynamic light scattering. Heterodomain interaction produced conformational rearrangements inferred by secondary structural change in circular dichroism, and validated by atomic force and transmission electron microscopy. Physical engagement of NBD1 with NBD2 translated into enhanced intrinsic ATPase activity. Molecular modeling delineated a complemental asymmetry of NBD1/NBD2 ATP-binding sites. Mutation in the predicted catalytic base residue, D834E of NBD1, altered NBD1 ATPase activity disrupting potentiation of catalytic behavior in the NBD1/NBD2 interactome. Thus, NBD1/NBD2 assembly, resolved by a panel of proteomic approaches, provides a molecular substrate that determines the optimal catalytic activity in SUR2A, establishing a paradigm for the structure-function relationship within the K ATP channel complex.

Inhibition of the ATPase activity of Escherichia coli ATP synthase by magnesium fluoride

Inhibition of ATPase activity of Escherichia coli ATP synthase by magnesium fluoride (MgFx) was studied. Wild-type F(1)-ATPase was inhibited potently, albeit slowly, when incubated with MgCl(2), NaF, and NaADP. The combination of all three components was required. Reactivation of ATPase activity, after removal of unbound ligands, occurred with half-time of approximately 14 h at 22 degrees C and was quasi-irreversible at 4 degrees C. Mutant F(1)-ATPases, in which catalytic site residues involved in transition state formation were modified, were found to be resistant to inhibition by MgFx. The data demonstrate that MgFx in combination with MgADP behaves as a tight-binding transition state analog in E. coli ATP synthase.

Peptides induce ATP hydrolysis at both subunits of the transporter associated with antigen processing

The transporter associated with antigen processing (TAP) plays a key role in the adaptive immune response by pumping antigenic peptides into the endoplasmic reticulum for subsequent loading of major histocompatibility complex class I molecules. TAP is a heterodimer consisting of TAP1 and TAP2. Each subunit is composed of a transmembrane domain and a nucleotide-binding domain, which energizes the peptide transport. To analyze ATP hydrolysis of each subunit we developed a method of trapping 8-azido-nucleotides to TAP in the presence of phosphate transition state analogs followed by photocross-linking, immunoprecipitation, and high resolution SDS-PAGE. Strikingly, trapping of both TAP subunits by beryllium fluoride is peptide-specific. The peptide concentration required for half-maximal trapping is identical for TAP1 and TAP2 and directly correlates with the peptide binding affinity. Only a background level of trapping was observed for low affinity peptides or in the presence of the herpes simplex viral protein ICP47, which specifically blocks peptide binding to TAP. Importantly, the peptide-induced trapped state is reached after ATP hydrolysis and not in a backward reaction of ADP binding and trapping. In the trapped state, TAP can neither bind nor exchange nucleotides, whereas peptide binding is not affected. In summary, these data support the model that peptide binding induces a conformation that triggers ATP hydrolysis in both subunits of the TAP complex within the catalytic cycle.

Energy transduction optical sensor in skeletal myosin

The skeletal myosin cross-bridge in dynamic association with actin is the unitary energy transducer in muscle, converting free energy from ATP hydrolysis into contractile force. Myosin's conserved ATP-sensitive tryptophan (AST) is an energy transduction optical sensor signaling transduction-related transient conformation change by modulating its fluorescence intensity amplitude and relaxation rate. Recently introduced techniques have provided the means of observing the time-resolved intensity decay from this single residue in the native protein to elucidate the mechanism of its ATP sensitivity. AST signal characteristics could be derived from local protein structure by a scenario involving interactions with excited-state tryptophan. This investigation suggests the very different possibility that hypochromism induced in the tryptophan absorption band, a ground-state effect, is a significant structural effector of optical transduction sensing. This possibility makes feasible the interpretation of the transient AST optical signal in terms of dynamical protein structure, thereby raising the empirical signal to the level of a structural determinant. Using the crystallographically based geometry from several myosin structures, the maximum calculated AST hypochromism is <10% to be compared with the value of approximately 30% observed here experimentally. Rationalizing the discrepancy invites further investigation of S1 dynamical structure local to the AST during transduction.

Myocardial function in rat genetic models of low and high aerobic running capacity

We recently evaluated treadmill aerobic running capacity in 11 inbred strains of rats and found that isolated working left ventricular function correlated (r = 0.86) with aerobic running capacity. Among these 11 strains the Buffalo (BUF) hearts produced the lowest and the DA hearts the highest isolated cardiac output. The goal of this study was to investigate the components of cardiac function (i.e., coronary flow, heart rates, stroke volume, contractile dynamics, and cross-bridge cycling) to characterize further the BUF and DA inbred strains as potential models of contrasting myocardial performance. Cardiac performance was assessed using the Langendorff-Neely working heart preparation. Isolated DA hearts were superior (P < 0.05) to the BUF hearts for cardiac output (63%), stroke volume (60%), aortic +dP/dt (47%), and aortic -dP/dt (46%). The mean alpha/beta-myosin heavy chain (MHC) isoform ratio for DA hearts was 21-fold higher relative to BUF hearts. At the steady-state mRNA level, DA hearts had a fivefold higher alpha/beta-ratio than the BUF hearts. The mean rate of ATP hydrolysis by MHCs was 64% greater in DA compared with BUF ventricles. These data demonstrate that the BUF and DA strains can serve as genetic models of contrasting low and high cardiac function.

Tyrosine mediated tryptophan ATP sensitivity in skeletal myosin

Myosin is the molecular motor in muscle that generates torque and transiently reacts with actin. The mechanical work performed by the motor occurs by successive decrements in the free energy of the myosin-nucleotide system. The seat of these transitions is the globular "head" domain of the myosin molecule (subfragment 1 or S1). A very useful (hitherto empirical) signal of these transitions has been optical, namely, detection of state-dependent changes in absorbance or fluorescence of S1. This effect has now been found to arise in a particular myosin residue (Trp510 in rabbit skeletal muscle), enabling the study of its intimate mechanism. In this work, based on measuring time-dependent signals, we find that the signal change upon nucleotide binding is adequately explained by assuming that nucleotide binding to a remote site causes a transition from a situation in which Trp510 is strongly statically quenched to a situation in which it is weakly statically quenched. The Trp510-static quencher interaction is also responsible, in part, for the changing tryptophan optical density in S1 upon nucleotide binding. Using crystallographically based geometry, calculation of the Trp510 electronic wave function indicates that Tyr503 is the static quencher.

The structure of Ap(4)A hydrolase complexed with ATP-MgF(x) reveals the basis of substrate binding

Ap(4)A hydrolases are Nudix enzymes that regulate intracellular dinucleoside polyphosphate concentrations, implicating them in a range of biological events, including heat shock and metabolic stress. We have demonstrated that ATP x MgF(x) can be used to mimic substrates in the binding site of Ap(4)A hydrolase from Lupinus angustifolius and that, unlike previous substrate analogs, it is in slow exchange with the enzyme. The three-dimensional structure of the enzyme complexed with ATP x MgF(x) was solved and shows significant conformational changes. The substrate binding site of L. angustifolius Ap(4)A hydrolase differs markedly from the two previously published Nudix enzymes, ADP-ribose pyrophosphatase and MutT, despite their common fold and the conservation of active site residues. The majority of residues involved in substrate binding are conserved in asymmetrical Ap(4)A hydrolases from pathogenic bacteria, but are absent in their human counterparts, suggesting that it might be possible to generate compounds that target bacterial, but not human, Ap(4)A hydrolases.

Isolating and localizing ATP-sensitive tryptophan emission in skeletal myosin subfragment 1

The fluorescence intensity difference between rabbit skeletal myosin subfragment 1 (S1) and nucleotide-bound or trapped S1 isolates ATP-sensitive tryptophans (ASTs) emission from the total tryptophan signal. Neutral (acrylamide) quenching of the ASTs is sensitive to the binding or trapping of nucleotide to the active site of S1. Anion (I(-)) quenching of the ASTs, sensitive to charge separation in the tryptophan micro environment, is negligible. These findings suggest the ASTs sense conformational change during ATPase from negatively charged surroundings. Specific chemical modifications of S1 identified the location of the ASTs. Trp131 was quenched by chemical modification, and its emission was isolated by taking the intensity difference between unmodified and modified S1. Trp131 fluorescence intensity and quenching constant do not distinguish among the bound or trapped nucleotides, suggesting that the vicinity of Trp131 does not change conformation during the ATPase cycle and eliminating Trp131 as an AST. Trp510 fluorescence was quenched by 5'-iodoacetamidofluorescein (5'IAF) modification of the reactive thiol (SH1) of S1. The tryptophan emission enhancement increment due to active site trapping decreases linearly with SH1 modification and extrapolates to 0 for 100% modification. These data identify Trp510 as the primary AST in skeletal S1 in agreement with observations from Dictyostelium (Batra and Manstein (1999) Biol. Chem. 380, 1017-1023) and smooth muscle S1 (Yengo et al. (2000) Biophys. J. 78, 242A). With Trp510 identified as the sole AST, fluorescence difference spectroscopy provides a novel means to monitor the concentration of myosin transient intermediates in ATP hydrolysis.